post "/register" do
  @users = all_users

  if valid_username?(params[:username]) &&
     valid_password?(params[:password], params[:confirm_pw])

    obj = create_user(params[:username], params[:password])
    create_user_yml(obj) # this is the method we need to create

    session[:success] = "User #{obj.user} created."
    redirect "/login"
  else
    session[:error] = "Try another username or ensure your passwords match."
    erb :register
  end
end